Semiconductor device

ABSTRACT

A semiconductor device includes: a semiconductor substrate having a main surface having an element formation region, a guard ring, a guard ring electrode, a channel stopper region, a channel stopper electrode, and a field plate disposed over and insulated from the semiconductor substrate. The field plate includes a first portion located between the main surface of the semiconductor substrate and the guard ring electrode, and a second portion located between the main surface of the semiconductor substrate and the channel stopper electrode. The first portion has a portion overlapping with the guard ring electrode when viewed in a plan view. The second portion has a portion overlapping with the channel stopper electrode when viewed in the plan view. In this way, a semiconductor device allowing for stabilized breakdown voltage can be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, in particular, to a semiconductor device having a guard ring.

2. Description of the Background Art

Generally, a power semiconductor requires a high main breakdown voltage retaining capability. For such retention of breakdown voltage, guard ring structures are generally utilized. Basic structures and applied structures thereof are disclosed in, for example, the following document or the like:

-   B. Jayant Baliga, “Power Semiconductor Devices”, the United States,     PWS PUBLISHING COMPANY, pp. 98-103

A guard ring structure is provided with an impurity region having a floating potential and surrounding an emitter to alleviate surface electric field and retain breakdown voltage.

If guard rings are provided up to the end of a semiconductor substrate, an electric field peak comes in the semiconductor substrate in the vicinity of its central portion in which an element formation region is provided. Hence, the guard rings are not formed up to the end of the semiconductor substrate.

Intervals between the guard rings are adjusted so that an electric field peak is maximal just below a guard ring electrode attached to an outermost guard ring. Unfortunately, this limits improvement of breakdown voltage just below the guard ring electrode attached to the outermost guard ring.

Also, the guard ring structure unfortunately requires a large area to retain breakdown voltage.

SUMMARY OF THE INVENTION

The present invention is made in light of the foregoing problem, and its object is to provide a semiconductor device allowing for stabilization of breakdown voltage.

A semiconductor device of the present invention includes: a semiconductor substrate having a main surface having an element formation region; a guard ring formed in the main surface of the semiconductor substrate to surround a circumference of the element formation region when viewed in a plan view; a guard ring electrode formed on the main surface of the semiconductor substrate and electrically connected to the guard ring; a channel stopper region formed in the main surface of the semiconductor substrate to be located external to the guard ring when viewed in the plan view; a channel stopper electrode formed on the main surface of the semiconductor substrate and electrically connected to the channel stopper region; and a field plate disposed over and insulated from the semiconductor substrate, the field plate including a first portion located between the main surface of the semiconductor substrate and the guard ring electrode, and a second portion located between the main surface of the semiconductor substrate and the channel stopper electrode, the first portion having a portion overlapping with the guard ring electrode when viewed in the plan view, the second portion having a portion overlapping with the channel stopper electrode when viewed in the plan view.

According to the present invention, the field plate includes the first portion located between the main surface of the semiconductor substrate and the guard ring electrode, and the second portion located between the main surface of the semiconductor substrate and the channel stopper electrode. When viewed in the plan view, the first portion has the portion overlapping with the guard ring electrode. When viewed in the plan view, the second portion has the portion overlapping with the channel stopper electrode. Accordingly, the field plate can be capacitively coupled to the guard ring electrode and the channel stopper electrode to prevent concentration of electric field just below the guard ring electrode attached to the outermost guard ring. As such, stabilized breakdown voltage can be achieved.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view schematically showing a semiconductor device in a first embodiment of the present invention.

FIG. 2 is a schematic cross sectional view taken along a line II-II of FIG. 1.

FIG. 3 is a plan view schematically showing a semiconductor device in a second embodiment of the present invention.

FIG. 4 is a schematic cross sectional view taken along a line IV-IV of FIG. 3.

FIG. 5 is a schematic cross sectional view of a semiconductor device in a third embodiment of the present invention, showing a cross section corresponding to line IV-IV of FIG. 3.

FIG. 6 is a schematic cross sectional view of a semiconductor device in a fourth embodiment of the present invention, showing a cross section corresponding to line IV-IV of FIG. 3.

FIG. 7 is a schematic cross sectional view of a semiconductor device of a comparative example, showing a cross section corresponding to line IV-IV of FIG. 3.

FIG. 8 shows surface electric field distribution (electric field and distance) in the first embodiment of the present invention and that in the comparative example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below with reference to figures.

First Embodiment

First, a configuration of a semiconductor device of a first embodiment of the present invention will be described.

Referring to FIG. 1 and FIG. 2, semiconductor device 20 of the present embodiment mainly has a semiconductor substrate 1, a collector electrode 5, a field oxide film 6, an emitter electrode 7 a, guard ring electrodes 7 b, 7 c, 7 d, 7 e, a channel stopper electrode 7 f, and field plates 9 a, 9 b, 10. For visibility, a passivation film 8 is not drawn in FIG. 1.

Referring to mainly FIG. 1, when viewed in a plan view, semiconductor device 20 has a central portion provided with a formation region 14 for a power semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor). When viewed in the plan view, guard ring electrodes 7 b, 7 c, 7 d, 7 e are formed to surround a circumference of element formation region 14. When viewed in the plan view, field plate 10 and channel stopper electrode 7 f are formed to surround the circumference of guard ring electrode 7 e.

Referring to mainly FIG. 2, semiconductor substrate 1 has an n⁻ substrate 1 b, a p-type embedded layer 2 a, guard rings 2 b, 2 c, 2 d, 2 e, a channel stopper region 3, and an n-type buffer layer 4. Semiconductor substrate 1 has a main surface 1 a. In main surface 1 a of semiconductor substrate 1, p-type embedded layer 2 a, guard rings 2 b, 2 c, 2 d, 2 e, and channel stopper region 3 are formed.

P-type embedded layer 2 a is formed in element formation region 14, and constitutes, for example, a base region of the IGBT. A boundary between p-type embedded layer 2 a and n ⁻ substrate 1 b forms a main junction.

Guard rings 2 b, 2 c, 2 d, 2 e are provided to retain breakdown voltage. Channel stopper region 3 is formed external to outermost guard ring 2 e. Channel stopper region 3 is provided to prevent a depletion layer from extending to the end of main surface 1 a.

On and over semiconductor substrate 1, field oxide film 6 and interlayer insulation film 12 are formed. Emitter electrode 7 a, guard ring electrodes 7 b, 7 c, 7 d, 7 e, and channel stopper electrode 7 f are formed on interlayer insulation film 12. Emitter electrode 7 a is electrically connected to p-type embedded layer 2 a via a contact hole provided in field oxide film 6 and interlayer insulation film 12.

Guard ring electrodes 7 b, 7 c, 7 d, 7 e are respectively electrically connected to guard rings 2 b, 2 c, 2 d, 2 e via contact holes formed in field oxide film 6 and interlayer insulation film 12. Channel stopper electrode 7 f is electrically connected to channel stopper region 3 via a contact hole provided in field oxide film 6 and interlayer insulation film 12.

Between field oxide film 6 and interlayer insulation film 12, field plates 9 a, 9 b are formed. Field plate 9 a (first portion) is located between main surface 1 a of semiconductor substrate 1 and guard ring electrode 7 e. When viewed in the plan view, field plate 9 a (first portion) has a portion 91 overlapping with guard ring electrode 7 e. Overlapping portion 91 and guard ring electrode 7 e constitute a capacitor C1.

Field plate 9 b (second portion) is located between main surface 1 a of semiconductor substrate 1 and channel stopper electrode 7 f. When viewed in the plan view, field plate 9 b (second portion) has a portion 92 overlapping with channel stopper electrode 7 f. Overlapping portion 92 and channel stopper electrode 7 f constitute a capacitor C4.

On interlayer insulation film 12, field plate 10 (third portion) is formed. Field plate 10 (third portion) belongs to the same layer as guard ring electrode 7 e and channel stopper electrode 7 f. In other words, field plate 10 (third portion), guard ring electrode 7 e, and channel stopper electrode 7 f are formed by the same layer made of, for example, aluminum.

Further, when viewed in the plan view, field plate 10 (third portion) has a portion 93 a overlapping with field plate 9 a (first portion). Overlapping portion 93 a and field plate 9 a constitute a capacitor C2. When viewed in the plan view, field plate 10 (third portion) has a portion 93 b overlapping with field plate 9 b (second portion). Overlapping portion 93 b and field plate 9 b constitute a capacitor C3.

Field plates 9 a, 9 b, 10 are electrically insulated from semiconductor substrate 1, guard ring electrode 7 e, and channel stopper electrode 7 f.

Guard rings 2 b, 2 c, 2 d, 2 e and guard ring electrodes 7 b, 7 c, 7 d, 7 e have floating potentials. Guard ring electrode 7 e and field plate 9 a, field plate 9 a and field plate 10, field plate 10 and field plate 9 b, and field plate 9 b and channel stopper electrode 7 f have floating potentials.

Capacitor C1 provides capacitance coupling of guard ring electrode 7 e and field plate 9 a. Capacitor C4 provides capacitance coupling of field plate 9 b and channel stopper electrode 7 f. Capacitor C2 provides capacitance coupling of field plate 9 a and field plate 10. Capacitor C3 provides capacitance coupling of field plate 9 b and field plate 10.

It should be noted that a distance between semiconductor substrate 1 and field plates 9 a, 9 b is preferably longer than a distance between field plates 9 a, 9 b and field plate 10. With this, the capacitance coupled between semiconductor substrate 1 and field plates 9 a, 9 b is smaller than the capacitance coupled between field plates 9 a, 9 b and field plate 10. This restrains the potentials of field plates 9 a, 9 b, 10 from fluctuating under an influence of the potential of main surface 1 a of semiconductor substrate 1.

Passivation film 8 is formed on emitter electrode 7 a, guard ring electrodes 7 b, 7 c, 7 d, 7 e, channel stopper electrode 7 f, field plate 10, and interlayer insulation film 12.

Semiconductor substrate 1 has a surface opposite to main surface 1 a. On this surface, n-type buffer layer 4 is formed. On n-type buffer layer 4, collector electrode 5 is formed.

Emitter electrode 7 a, guard ring electrodes 7 b, 7 c, 7 d, 7 e, channel stopper electrode 7 f, and field plate 10 are formed of, for example, aluminum. Field plates 9 a, 9 b are formed of, for example, polycrystalline silicon. Materials therefor are not limited to the materials exemplified above. They may be formed of different materials.

The configuration of semiconductor device 20 can be formed using a process flow for a general semiconductor such as an IGBT. For example, a step of embedding a gate electrode and a step of forming an emitter electrode in the process flow can be applied.

Next, an operation of a semiconductor device of the present embodiment will be described.

In semiconductor device 20 of the present embodiment, capacitor C1 provides capacitance coupling between guard ring electrode 7 e and field plate 9 a. Capacitor C4 provides capacitance coupling between field plate 9 b and channel stopper electrode 7 f. Capacitor C2 provides capacitance coupling between field plate 9 a and field plate 10. Capacitor C3 provides capacitance coupling between field plate 9 b and field plate 10.

In this way, capacitors C1-C4 provide capacitance coupling of guard ring electrode 7 e, field plates 9 a, 9 b, 10, and channel stopper electrode 7 f. Guard ring electrode 7 e, field plate 9 a, 9 b, 10, and channel stopper electrode 7 f have higher potentials as they are located more outwardly.

Since semiconductor device 20 of the present embodiment is provided with the plurality of guard rings 2 b, 2 c, 2 d, 2 e, the depletion layer first extends toward guard ring 2 b. This alleviates electric field at a corner portion of the main junction located at the boundary between p-type embedded layer 2 a and n ⁻ substrate 1 b. Then, the depletion layer extends toward guard ring 2 c, thereby alleviating electric field just below guard ring electrode 7 b attached to guard ring 2 b. In this way, the plurality of guard rings 2 b, 2 c, 2 d, 2 e allow the depletion layer to extend toward outermost guard ring 2 e, thus alleviating electric field.

In this case, an electric field peak is supposed to come just below guard ring electrode 7 e attached to outermost guard ring 2 e. However, field plates 9 a, 9 b, 10 alleviate concentration of electric field just below guard ring electrode 7 e attached to outermost guard ring 2 e, thus stabilizing the surface potential of semiconductor substrate 1.

The following explains functions and effects of the semiconductor device of the present embodiment in comparison to a comparative example.

Referring to FIG. 7, a semiconductor device of the comparative example is different from that of the present embodiment mainly in that no field plates 9 a, 9 b, 10 are formed. In semiconductor device 20 of the comparative example, a maximal electric field peak comes at a point X just below guard ring electrode 7 e attached to outermost guard ring 2 e.

Referring to FIG. 8, a solid line therein represents distribution of surface electric field of the semiconductor device of the comparative example. A broken line in FIG. 8 represents distribution of surface electric field of the semiconductor device of the present embodiment. The indication of point X therein represents electric field and a distance of point X located just below guard ring electrode 7 e attached to outermost guard ring 2 e of FIG. 7. As shown in FIG. 8, in the comparative example, an electric field peak is maximal at point X.

In contrast, semiconductor device 20 of the present embodiment is provided with field plates 9 a, 9 b, 10 formed external to guard ring electrode 7 e attached to outermost guard ring 2 e. In addition, capacitors C1-C4 provide capacitance coupling of guard ring electrode 7 e, field plates 9 a, 9 b, 10, and channel stopper electrode 7 f. This alleviates electric field exerted just below guard ring electrode 7 e attached to outermost guard ring 2 e, thereby preventing concentration of electric field. Thus, breakdown voltage can be increased. In this way, stabilized breakdown voltage is achieved. As shown in FIG. 8, an electric field peak is not maximal just below guard ring electrode 7 e attached to outermost guard ring 2 e.

In addition, semiconductor device 20 of the present embodiment achieves stabilized electric field between outermost guard ring 2 e and channel stopper region 3. Accordingly, the width between outermost guard ring 2 e and channel stopper region 3 can be narrowed to achieve reduction of the area of semiconductor substrate 1.

Second Embodiment

A semiconductor device of a second embodiment of the present invention is different from the semiconductor device of the first embodiment mainly in configurations of field plates.

Referring to FIG. 3 and FIG. 4, semiconductor substrate 1 has a main surface 1 a over which field plates 9 a, 9 b are formed with a field oxide film 6 interposed between main surface 1 a and field plates 9 a, 9 b. For visibility, in FIG. 3, a passivation film 8 is not drawn.

Formed on field plates 9 a, 9 b is an insulation film 13 on which a field plate 9 c (third portion) is formed. On field plate 9 c, an interlayer insulation film 12 is formed. On interlayer insulation film 12, a guard ring electrode 7 e and a channel stopper electrode 7 f are formed. In other words, field plate 9 c (third portion) is formed as a layer below guard ring electrode 7 e and channel stopper electrode 7 f.

When viewed in a plan view, field plate 9 c (third portion) has a portion 93 a overlapping with field plate 9 a (first portion). Overlapping portion 93 a and field plate 9 a constitute a capacitor C2. When viewed in the plan view, field plate 9 c (third portion) has a portion 93 b overlapping with field plate 9 b (second portion). Overlapping portion 93 b and field plate 9 b constitute a capacitor C3.

Field plate 9 c is formed of, for example, polycrystalline silicon doped with an impurity in high concentration.

Other configurations of the present embodiment are similar to those of the foregoing first embodiment. Hence, the same elements are given the same reference characters and will not be described repeatedly.

The configuration of semiconductor device 20 can be formed using a process flow for a general semiconductor. Semiconductor device 20 can be formed to have a desired structure, by forming field plates 9 a, 9 b and field plate 9 c as two layers with insulation film 13 interposed therebetween.

With this, the semiconductor device of the present embodiment provides functions and effects similar to those of the first embodiment.

Since field plates 9 a, 9 b, 9 c are formed to be contained by field oxide film 6, interlayer insulation film 12, and insulation film 13, voltage fluctuations resulting from aluminum slide, which causes a problem in a resin-molded chip, can be prevented. The term “aluminum slide” herein refers to peel-off or displacement of an aluminum wire caused by a force exerted thereon and resulting from a thermal stress arising from a difference in thermal expansion coefficient from the resin.

Third Embodiment

A semiconductor device of a third embodiment of the present invention is different from the semiconductor device of the first embodiment in configurations of field plates.

Referring to FIG. 5, semiconductor substrate 1 has a main surface 1 a over which field plates 9 a, 9 b are formed with a field oxide film 6 interposed between main surface 1 a and field plates 9 a, 9 b. Field plates 9 c (third portion) are formed between field plates 9 a, 9 b and an interlayer insulation film 12 is provided among them. In the present embodiment, two field plates 9 c (third portion) are described but the present invention is not limited to this. A single or a plurality of field plates 9 c may be provided. Field plates 9 a, 9 b, 9 c are arranged along a direction in which main surface 1 a of semiconductor substrate 1 extends. Field plates 9 a, 9 b, 9 c overlap with their adjacent field plates 9 a, 9 b, 9 c in the direction in which main surface 1 a extends.

In the direction in which main surface 1 a extends, field plates 9 c (third portion) have a portion 93 a overlapping with field plate 9 a (first portion). Overlapping portion 93 a and field plate 9 a constitute a capacitor C2. In the direction in which main surface 1 a extends, field plates 9 c (third portion) have a portion 93 b overlapping with field plate 9 b (second portion). Overlapping portion 93 b and field plate 9 b constitute a capacitor C3. In the direction in which main surface 1 a extends, field plates 9 c (third portion) have portions 93 c overlapping with each other. Overlapping portions 93 c thereof constitute a capacitor C5.

Field plates 9 c are formed of, for example, polycrystalline silicon doped with an impurity in high concentration.

The other configurations of the present embodiment are similar to those of the foregoing first embodiment. Hence, the same elements are given the same reference characters and will not be described repeatedly.

The configuration of semiconductor device 20 can be formed using a process flow for a general semiconductor and field plates 9 a, 9 b and field plate 9 c can be formed as one layer.

As such, the semiconductor device of the present embodiment provides functions and effects similar to those of the first embodiment.

Field plates 9 a, 9 b, 9 c are formed to be contained by field oxide film 6 and interlayer insulation film 12, and voltage fluctuations resulting from aluminum slide can be prevented.

In addition, since field plates 9 a, 9 b and field plate 9 c can be formed as one layer, the number of steps in the process can be reduced to achieve simplified process steps.

Fourth Embodiment

A semiconductor device of a fourth embodiment of the present invention is different from the semiconductor device of the first embodiment in configurations of field plates.

Referring to FIG. 6, field plates 9 a (first portion), 9 b (second portion), 9 c (third portion) include embedded upper-layer electrodes 11 a and lower-layer electrodes 11 b. Embedded upper-layer electrodes 11 a are provided in contact with the top of lower-layer electrodes 11 b.

Semiconductor substrate 1 has a main surface 1 a over which respective lower-layer electrodes 11 b of field plates 9 a, 9 b, 9 c are formed with a field oxide film 6 interposed between main surface 1 a and lower-layer electrodes 11 b. Lower-layer electrodes 11 b are provided adjacent to one another with an insulation film 13 interposed therebetween. Embedded upper-layer electrodes 11 a are formed in contact with the top of lower-layer electrodes 11 b. Embedded upper-layer electrodes 11 a are provided adjacent to one another with an interlayer insulation film 12 interposed therebetween.

In the present embodiment, two field plates 9 c (third portion) are described but the present invention is not limited to this. A single or a plurality of field plates 9 c may be provided. Field plates 9 a, 9 b, 9 c are arranged along a direction in which main surface 1 a of semiconductor substrate 1 extends.

In the direction in which main surface 1 a extends, field plates 9 c (third portion) have a portion 93 a overlapping with field plate 9 a (first portion). Overlapping portion 93 a and field plate 9 a constitute a capacitor C2. In the direction in which main surface 1 a extends, field plates 9 c (third portion) have a portion 93 b overlapping with field plate 9 b (second portion). Overlapping portion 93 b and field plate 9 b constitute a capacitor C3. Further, in the direction in which main surface 1 a extends, field plates 9 c (third portion) have portions 93 c overlapping with each other. Overlapping portions 93 c thereof constitute a capacitor C5.

Each of embedded upper-layer electrodes 11 a of field plates 9 a, 9 b may be provided on a portion of the top of each of lower-layer electrodes 11 b or on the entire portion of the top thereof. If each of embedded upper-layer electrodes 11 a is provided on the entire portion of the top of each of lower-layer electrodes 11 b, an electrical capacitance of guard ring electrode 7 e and field plate 9 a as well as an electrical capacitance of channel stopper electrode 7 f and field plate 9 b can be large. It is not to say that a larger electrical capacitance is better, and the electrical capacitances can be determined in consideration of whole conditions such as distribution of electric field.

Embedded upper-layer electrodes 11 a are insulated by field oxide film 6, interlayer insulation film 12, and insulation film 13 but may have a portion connected to the passivation film.

The other configurations of the present embodiment are similar to those of the foregoing first embodiment. Hence, the same elements are given the same reference characters and will not be described repeatedly.

The configuration of semiconductor device 20 can be formed using a process flow for a general semiconductor, and embedded upper-layer electrodes 11 a can be formed in contact with the tops of lower-layer electrodes 11 b.

As such, the semiconductor device of the present embodiment provides effects and functions similar to those of the first embodiment.

In addition, field plates 9 a, 9 b, 9 c are formed to be contained by field oxide film 6, interlayer insulation film 12, and insulation film 13, whereby voltage fluctuations resulting from aluminum slide can be prevented.

Further, field plates 9 a, 9 b, 9 c are made up of two layers, i.e., embedded upper-layer electrodes 11 a and lower-layer electrodes 11 b, which facilitates increasing in thickness a portion therein opposite to the direction along main surface 1 a of semiconductor substrate 1. This allows for an enlarged area in which field plates 9 a, 9 b, 9 c face one another, thereby achieving stabilization of breakdown voltage.

The embodiments described above can be combined appropriately.

The present invention can be applied beneficially in particular to a semiconductor device having a guard ring.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims. 

What is claimed is:
 1. A semiconductor device, comprising: a semiconductor substrate having a main surface having an element formation region at a center of the semiconductor substrate; a plurality of guard ring electrodes formed on said main surface of said semiconductor substrate to surround a circumference of said element formation region when said plurality of guard ring electrodes and said element formation region is viewed from a plan view; a plurality of guard rings formed in said main surface of said semiconductor substrate and electrically connected, respectively, to said plurality of guard ring electrodes; a channel stopper electrode formed on said main surface of said semiconductor substrate to be located outside of said plurality of guard ring electrodes when said channel stopper electrode and said plurality of guard ring electrodes are viewed in the plan view; a channel stopper region formed in said main surface of said semiconductor substrate and electrically connected to said channel stopper electrode; and a field plate disposed over and insulated from said semiconductor substrate, said field plate including a first portion disposed to surround a circumference of an outermost guard ring electrode of the plurality of guard ring electrodes when said first portion and the plurality of guard ring electrodes are viewed from the plan view, said field plate including a second portion located between said main surface of said semiconductor substrate and the outermost guard ring electrode, and a third portion located between said main surface of said semiconductor substrate and said channel stopper electrode, said second portion having a portion overlapping with the outermost guard ring electrode when viewed in a cross-section view, said third portion having a portion overlapping with said channel stopper electrode when viewed in the cross-section view.
 2. The semiconductor device according to claim 1, wherein: said first portion has a portion overlapping with at least one of said second portion and said third portion when viewed in the cross-section view.
 3. The semiconductor device according to claim 2, wherein said first portion of said field plate, the outermost guard ring electrode, and said channel stopper electrode are formed of a same layer.
 4. The semiconductor device according to claim 1, wherein: said main surface extends in a first direction, and said second portion, said third portion, and said first portion are arranged along the first direction.
 5. The semiconductor device according to claim 1, wherein said field plate is capacitively coupled to the outermost guard ring electrode and is capacitively coupled to said channel stopper electrode.
 6. The semiconductor device according to claim 1, wherein said field plate does not overlap said plurality of guard rings.
 7. The semiconductor device according to claim 1, wherein said field plate is disposed between an outermost one of said plurality of guard rings and an outer edge of said semiconductor device. 